Aluminum alloys that are used in wheel structures for aircraft include Aluminum Association Series alloys 2014-T6, 2040-T6 and 7050-T74. These alloys are specific alloys within the Aluminum Association Series of alloy classes 2XXX and 7XXX, respectively. These alloys are attractive due to their high strength and fracture toughness characteristics. Although the 2XXX and 7XXX aluminum alloys exhibit high strength characteristics they are more prone to corrosion than other aluminum alloys. This corrosion includes general corrosion, pitting, stress corrosion cracking, and intergranular attack.
A useful method for dealing with the corrosion of aluminum surfaces in aircraft wheel structures involves the application of a sulfuric acid anodic coating in combination with a sodium dichromate sealant to the aluminum surface followed by the application of a chromated epoxy primer and a polyurethane topcoat. However, a problem with this method relates to the fact that current maintenance practices for aircraft wheels require a fluorescent penetrant inspection (FPI) during every major overhaul. In order to perform this inspection, the paint must be stripped. Following inspection the paint is then reapplied. The task of stripping and reapplying the paint for FPI inspection during maintenance and overhaul is labor intensive and may involve the use of environmentally polluting materials.
The problem therefore is to provide these wheel structures with protection from corrosion without having to employ such stripping and reapplication procedures. This invention, in at least one embodiment, provides a solution to this problem. In one embodiment, the invention provides wheel corrosion protection that achieves a reduction in maintenance costs and avoids the use of environmentally polluting materials. The corrosion protection provided by this invention is also applicable to other aluminum articles.